Ref T13249. Ref T13258. In some cases, builds are not idempotent and should not be restarted casually.

If the scary part is at the very end (deploy / provision / whatever), it could be okay to restart them if they previously failed.

Also, make the "reasons why you can't restart" and "explanations of why you can't restart" logic a little more cohesive.

• Tried to restart builds in various states (failed/not failed, restartable always/if failed/never, already restarted), got appropriate errors or restarts.
• (I'm not sure the "Autoplan" error is normally reachable, since you can't edit autoplans to configure things to let you try to restart them.)